From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id D6FE0C433EF for ; Mon, 7 Mar 2022 12:23:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S242219AbiCGMYq (ORCPT ); Mon, 7 Mar 2022 07:24:46 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51862 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S242225AbiCGMYX (ORCPT ); Mon, 7 Mar 2022 07:24:23 -0500 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0300763EF for ; Mon, 7 Mar 2022 04:23:27 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 6BDA7B811B8 for ; Mon, 7 Mar 2022 12:23:26 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 05B09C340F5; Mon, 7 Mar 2022 12:23:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1646655805; bh=4FU9MVXnmckZgKV5S9qqzP2l0zaOcBmfWx7Vs1t8lqI=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=FEyVbZ3OMoFOMHm9xiM2pbQmIdXKk8PQB+ppsCAu2MUeqmRpvHUqFoU/CLCEYw7zR IW187SpKnAxUn/r0+sVcC5P3uqJb8IupAzV2EChROuAsqQmZJTi1s+h+ctBvpcsISR j6E5jRMUTvxdZSsCZNXhABPUzEp4RNauUWVoW7vhkF5FC5JqoRY3mwkZU8c4GexMYD ffbgyPgcFja6Zjep/wIoV2XGW/gynERjEL2UT/BMc9avTRtDttOlYGmrHAFRTN2W0Q 2D/60vehzS3COdMqIGoQe8wAS4ZBha4eTi1N1HXoilcsq4UuQWqHu/m1ayNRLSr1Sx 9IjrrmlIU4PgQ== Received: from sofa.misterjones.org ([185.219.108.64] helo=why.misterjones.org) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94.2) (envelope-from ) id 1nRCOW-00CmSd-DG; Mon, 07 Mar 2022 12:23:21 +0000 Date: Mon, 07 Mar 2022 12:23:20 +0000 Message-ID: <87bkyi0x53.wl-maz@kernel.org> From: Marc Zyngier To: Rongwei Wang Cc: catalin.marinas@arm.com, will@kernel.org, joey.gouly@arm.com, mark.rutland@arm.com, akpm@linux-foundation.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH RFC] arm64: improve display about CPU architecture in cpuinfo In-Reply-To: References: <20220307030417.22974-1-rongwei.wang@linux.alibaba.com> <87h78a178u.wl-maz@kernel.org> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/27.1 (x86_64-pc-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII X-SA-Exim-Connect-IP: 185.219.108.64 X-SA-Exim-Rcpt-To: rongwei.wang@linux.alibaba.com, catalin.marinas@arm.com, will@kernel.org, joey.gouly@arm.com, mark.rutland@arm.com, akpm@linux-foundation.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 07 Mar 2022 12:13:50 +0000, Rongwei Wang wrote: > > > > On 3/7/22 4:45 PM, Marc Zyngier wrote: > > On Mon, 07 Mar 2022 03:04:17 +0000, > > Rongwei Wang wrote: > >> > >> Now, it is unsuitable for both ARMv8 and ARMv9 to show a > >> fixed string "CPU architecture: 8" in /proc/cpuinfo. > > > > Please read the various threads that have been going on over the past > > 10+ years about *why* we don't allow this sort of change (TL;DR: it > > breaks userspace, and we don't do that). > > > > Also, there is no material difference between v8 and v9 that would be > > observable from userspace outside of the "Features:" line. And if that > > doesn't convince you, just think of '8' as the number of bytes > > used by > I got your point. It seems that we can regard '8' as the number of > bytes. But what make me do this is that 'CPU architecture: 8' is > confusing, especially those responsible for testing. > And I believe that most people regard this '8' as ARMv8, maybe not. That was the original intention. But given that there is no userspace visible difference between v8, v9 and whatever comes after it, this is a pointless change. My comment about the size of a VA was just a joke, and not something to be taken seriously. > In fact, I'm not sure it has potential ABI implications, so seek your > advice. Plenty of userspace programs parse /proc/cpuinfo. If you replace '8' with anything else, they will fail. Which is why although your patch makes sense, it comes 10 years too late, and we can't change this anymore. Thanks, M. -- Without deviation from the norm, progress is not possible.